The magnetic field dependence of the nuclear spin-lattice relaxation rate constant, also called the magnetic relaxation dispersion (MRD), reports the power density of fluctuations created by intra- and inter-molecular motions as a function of the nuclear Larmor frequency, which may be varied from 5 kHz to 500 MHz for 1H. The use of paramagnetic contributions to the nuclear relaxation extends the effective frequency range to 0.3 THz or time scales of order 1 ps. Combined with appropriate statistical theories, the MRD profiles provide a powerful method for studying molecular dynamics, protein dynamics in particular, and factors that modify nuclear spin relaxation such as relaxation agents used in MRI. This laboratory has assembled unique instrumentation for MRD measurements. We propose to: characterize the dynamics of internally trapped water molecules in proteins based on MRD data from rotationally immobilized proteins;define the role of membrane- bound proteins in controlling water spin-lattice relaxation in membrane model systems;extend the spin-fracton relaxation theory to the case of quadrupolar spins, deuterium and nitrogen-14, to test the generality of the theory and the implications for energy redistribution in proteins;measure the high frequency motions of water adjacent to specific paramagnetic centers in proteins;define the conditions for maximum water-proton relaxivity for metal chelate and organic radicals conjugated to rotationally immobilized proteins, which is important in understanding how targeted MRI contrast agents can work;measure accurate relaxation dispersion profiles for excised tissue systems from 10 kHz to 500 MHz to provide complete data sets for comparison with much more scattered experiments accumulated in a clinical setting;measure 31P and 13C MRD profiles for commonly observed metabolites in a model tissue matrix to provide an understanding of the relaxation mechanisms over a wide field range;measure the MRD profiles and test the spin-fracton relaxation theory for DNA as a model stiff linear system;measure the MRD profiles for specific intramolecular vectors in proteins using direct detection of protein spins;and use zinc and calcium metal sites in carbonic anhydrase II and the C2A domain of synaptotagmin I in combination with nitroxide labeled cysteine mutants to measure complete MRD profiles of these specifically defined intramolecular vectors. The results of these studies have direct bearing on how we understand energy redistribution in proteins or how structural disturbances propagate through the structure as a possible component of function. There are immediate applications of this work in the context of clinical magnetic imaging, both in extracting additional information from existing approaches and the development of new classes of targeted contrast agents. This project will use measurements of nuclear spin-lattice relaxation rate constants to deduce the nature of intra and inter-molecular motions in proteins that affect contrast in MRI and the information that may be obtained from in vivo magnetic resonance protocols. Included are studies targeted spin-relaxation or contrast agents for MRI that are fundamentally different in design and action from presently used soluble contrast agents. The molecular biophysical foundations of this work are important for understanding the functional role of protein dynamics.